i drove a base model IS 300h from 2014 for 3 weeks until my new IS300h F-sport was ready so i can compare the 2. I first noticed the strange noise combined with vibrations from the diveshaft? when driving on the highway in heavy traffic doing 40/50mph for at least 20km. the engine is humming just over idle rpm and the system constantly switches between petrol and electric. when the petrol kicks in the sound is there and oh boy did that het irritate. mainly because the cabin is so quiet ( i recently drove a jag xkr 8cyl convertible and when you accellerate it vibrates, rattles, sniffs, shakes but here it is called character... ). from that moment on i always noted that sound and i could onluyhope my car would be better.
and it is. the new 2015 does have it but much shorter. it is more or les bearable. but is still wonder why Lexus brought this car to market with this phenomena. i sometimes think it was marketed too soon and development was not finished yet.. i am sure they knew and maybe that is also the reason the IS300H is not for sale in the states?..